The use of radiation-sensitive functionality to .induce crosslinking of a polymeric material is an advancing art. Incorporating radiation crosslinkable functionality into elastomeric polymers is desirable since elastomers containing such functionality could be utilized to produce solvent free products and processes including but not limited to pressure-sensitive adhesives (PSA's), coatings, laminates, membranes sealants and lithographic applications. Such radiation cured polymers exhibit cohesive strength, and enhanced resistance to temperature, abrasion, solvents and ozone.
Applications or methods employing external, added or blended crosslinking reagents have inherent difficulties. Added reagents can be toxic and/or volatile and can present manufacturing difficulties and hazards. A crosslinking agent that is incompatible with the elastomeric backbone may also hinder effective crosslinking. Reactive unsaturation sites in the polymeric backbone can facilitate external free-radical crosslinking, but depending on the polymer, the unsaturation also provides sites at which the backbone can be degraded by reactions involving radicals.
It is desirable to have pressure-sensitive adhesives and coatings which are curable without the use of these additive compounds yet have saturated polymeric backbones which are not degraded in reactions involving radicals. To this end, radiation-reactive crosslinking agents may alternatively be incorporated into the polymer backbone, for instance, by copolymerizing with a radiation-sensitive vinyl polymerizable comonomer. However, preparing such comonomers on a large scale is generally difficult. Radiation-reactive functionality may also be grafted onto the polymer backbone in a post-polymerization step, however, the resulting polymer is typically a heterogeneous product of low yield due to the difficulty of achieving adequate molecular contact at desired reaction sites. A good discussion of the mechanisms of photochemical reactions in polymers and examples of photoinitiators may be found in J. F. Rabek, "Mechanisms of Photophysical Processes and Photochemical Reactions in Polymers, Theory and Applications," Chapters 11 and 12, J. Wiley & Sons, 1987, which is hereby incorporated herein by reference.
U.S. Pat. Nos. 4,188,215 to Sato et al.; 3,923,703 to Fukutani et al.; 3,867,318 to Nishikubo et al.; 3,694,383 to Azami et al.; and 3,560,465 to Reynolds; and U.K. Patent 1,341,004 all relate to polymeric resins incorporating photosensitive functionality and/or processes for making such resins. These photosensitive resins are generally useful in photographic films.
Photosensitive coatings comprising a blend of a polymer and a photosensitive crosslinking agent are disclosed in U.S. Pat. No. 3,867,271 to Malatesta, et al. In this patent, a conjugated diene containing Butyl rubber is cured by ultraviolet radiation with the aid of certain photosensitizers. A similar composition said to be useful as a coating for glass substrates is disclosed in U.S. Pat. No. 4,086,373 to Tobias et al., as comprising at least a rubbery thermoplastic organic polymer and an organic photosensitizer.
Photosensitive vinyl monomers are disclosed in U.S. Pat. Nos. 3,429,852 and 3,574,617 both to Skoultchi, wherein ethylenically unsaturated derivatives of substituted benzophenones are prepared by a method involving reacting a substituted benzophenone with an ethylenically unsaturated reagent such as glycidyl acrylate or glycidyl methacrylate. The resulting monomers may thereafter be homo- or copolymerized with a variety of conventional ethylenically unsaturated, i.e. vinyl, monomers. Photosensitive coating systems are prepared by depositing a solid polymer from an organic solvent or an emulsion onto a substrate. The photosensitive coating are said to be particularly suitable for use in various applications including, for example, lithography and chemical milling.
A similar concept is disclosed in U.S. Pat. No. 4,148,987 to Winey, wherein monoethylenically unsaturated derivatives of substituted benzophenones or acetophenones are prepared by a reaction of the benzophenone or acetophenone with a vinyl benzyl halide. These derivatives are polymerizable to form homopolymers, or copolymers with a wide variety of conventional ethylenically unsaturated monomers. The resulting polymers are sensitive to radiation, such as ultraviolet light having a wavelength of 2,000 to 5,000 Angstroms, and readily crosslink or cure upon exposure to such radiation. Adhesives, binders, coatings and impregnating compositions are made from the polymers.
Radiation-sensitive functionality has also been used to induce crosslinking of a polymeric material in the printing industries where printing plates are initially coated with polymers having light sensitivity. Such radiation-crosslinkable polymers have also been widely used as photoresists in the manufacture of semi-conductors or other engraved articles.
The chemical modification of poly(vinylbenzylchloride) with a photosensitive compound including p-hydroxybenzophenone, 2-hydroxyfluorenone, potassium carbazole, and the like is disclosed in Bailey, et al., Journal of Applied Polymer Science: Polymer Chemistry Edition, vol. 17, 777-782 (1979).
In commonly assigned U.S. Ser. No. 441,575, filed Nov. 22, 1989, which is also a continuation-in-part of co-pending U.S. Ser. No. 416,503 filed Oct. 3, 1989, which is a continuation-in-part of co-pending U.S. Ser. No. 199,665 filed May 27, 1988; and co-pending U.S. Ser. No. 416,713 filed Oct. 3, 1989, which is a continuation-in-part of U.S. Ser. No. 199,665 filed May 27, 1988, the disclosures of which are hereby incorporated by reference, it was theorized that the introduction of controlled amounts of the desired specific functionality as pendant groups on the saturated hydrocarbon backbone would greatly extend usefulness by permitting these polymers to be adhered to other surfaces and/or to be co-reacted with or compatibilized with other functional polymers by "grafting" or crosslinking reactions. It was further theorized that the introduction of pendant functionality of the right type and amounts would permit these saturated hydrocarbon polymers to be "painted" or coated with or on other materials, and/or to be laminated with or dispersed in other materials to yield composite materials with a desired combination of properties.
Commonly assigned U.S. Ser. No. 442,028, filed Nov. 27, 1989, and U.S. Ser. Nos. 631,610 and 633,645, both filed Dec. 20, 1990, all of which are incorporated herein by reference, disclose radiation reactive functionalized copolymers comprising an isoolefin having about 4 to about 7 carbon atoms and a para-alkylstyrene, wherein a radiation-reactive functional group is attached to the para-alkyl group of the para-alkylstyrene.
Previous workers have not applied nucleophilic substitution reactions to isobutylene/para-methyl-styrene/para-bromomethylstyrene terpolymers to produce versatile, thermally stable, radiation curable, substantially backbone-saturated, pendant acrylate/photosensitizer-functionalized, soluble copolymers.